Method and network-side device for optimizing activation/deactivation of ISR

ABSTRACT

The present application relates to mobile communication technical field, and a method for optimizing activation/deactivation Idle State signaling Reduction (ISR) and a network side device are disclosed. The method includes: during a process of updating User Element (UE) area, a first network entity, when receiving a context request message transmitted from a second entity, determines to activate or deactivate ISR, according to a mobile-reachable timer or an implicit detach timer corresponding to said UE, or operation states of the mobile-reachable timer and the implicit detach timer; and the first network entity transmits the determination result to the second network entity, said second network entity determines to instruct the UE to activate or deactivate the ISR according to the received determination result. The application optimizes the existing procedure for the activating/deactivating of the ISR, enables the ISR processing at the network side and the UE side to be consistent in height, and thus avoiding unnecessary signaling expense.

The present application is a US National Stage of InternationalApplication No. PCT/CN2011/075576, filed 10 Jun. 2011, designating theUnited States, and claiming claims priority to Chinese PatentApplication No. 201010209863.1, filed with the State IntellectualProperty Office of China on Jun. 18, 2010 and entitled “Method andnetwork-side device for optimizing activation/deactivation of ISR”,which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of mobile communications andparticularly to a method and network-side device for optimizingactivation/deactivation of ISR, an ISR operation method at the UserEquipment (UE) side and a LIE.

BACKGROUND OF THE INVENTION

Idle State Signalling Reduction (ISR) is a technology to reduce idlestate signalling in an Evolved Packet System (EPS) so as to alleviate asignalling load between a User Equipment (UE) in an idle state and anetwork.

A Serving GPRS Support Node (SGSN, where GPRS stands for General PacketRadio Service) is a network entity in a Universal Terrestrial RadioAccess Network (UTRAN), and a Mobility Management Entity (MME) is anetwork entity in an Evolved Universal Terrestrial Radio Access Network(E-UTRAN).

When the UE registers with both the MME in the E-UTRAN and the SGSN inthe UTRAN and activates ISR, the UE in an idle state will not performsignalling interaction with the network side while the UE resides andmoves in a Tracking Area (TA) in a list of Tracking Area IDs (TAIs)registered in the E-UTRAN and a Routing Area (RA) registered in theUTRAN.

Activation of ISR is controlled at the network side, and when the UE inan idle state initiates a Tracking Area Update (TAU) or Routing AreaUpdate (RAU) procedure in the E-UTRAN or the UTRAN, the MME or the SGSNinstructs the UE to activate or deactivate ISR in a TAU Accept messageor an RAU Accept message, and the UE activates or deactivates ISR inresponse to the instruction. An initial value of a Temporary Identityused in Next update (TIN) is set by the UE upon successful attachment.The UE resets the TIN to a Globally Unique Temporary Identity (GUTI)regardless of original value thereof upon successful initial attachmentto the E-UTRAN. The UE resets the TIN to a Packet Temporary MobileStation Identity (P-TMSI) regardless of original value thereof uponsuccessful initial attachment to the GERAN/UTRAN. The UE has to set alocally stored TIN to a GUTI or a P-TMSI regardless of original valuethereof upon reception of the TAU Accept message or the RAU Acceptmessage instructing ISR to be deactivated. With the TAU Accept messageinstructing ISR to be activated, the UE decides setting of the TINdependent upon the value of the TIN. If the value of the TIN is a P-TMSIor a Radio Access Type related TMSI (RAT-related TMSI), the TIN is setto the RAT-related TMSI, and if the value of the TIN is a GUTI, thevalue of the TIN is set to the GUTI. With the RAU Accept messageinstructing ISR to be activated, the UE decides setting of the TINdependent upon the value of the TIN if the value of the TIN is a GUTI oran RAT-related TMSI, the TIN is set to the RAT-related TMSI, and if thevalue of the TIN is a P-TMSI, the value of the TIN is set to the P-TMSI.Noted the value of the TIN is merely for the purpose of distinguishing.

In this context, “area update” broadly refers to “tracking area update”or “routing area update”. The following description will be given by wayof an example in which a UE firstly is attached to a network over aUTRAN and then accesses an E-UTRAN to initiate a TAU procedure. Asillustrated in FIG. 1, the TAU procedure is as follows.

The UE determines that a TAU trigger condition is satisfied when the UEaccesses a TA in the E-UTRAN from an RA in the UTRAN and the triggers aTAU to be started (the step S101); the UE initiates a Tracking AreaUpdate Request to an MME (the step S102 to the step S103); since the UEis registered with an old S4 SGSN (one type of SGSN supporting ISR; andSGSN in this context generally refers to the S4-SGSN), the new MMEretrieves context information of the UE from the old SGSN (the stepS104, the step S105 and the step 107); then the MME instructs a ServingGateway (GW)/a Packet Data Network Gateway (PDN GW) to modify bearerinformation of the UE (the step S109 to the step S113); the MMEtransmits a Location Update Request to an HSS to instruct the HSS tocancel location information of the UE in the old SGSN (the step S114 tothe step S116); the old SGSN releases an Iu interface connection (thestep S117 and the step S118); the HSS returns a Location Update Responsemessage to the MME (the step S119); and the MME returns a Tracking AreaUpdate Accept Message to the UE to thereby finish the tracking areaupdate (the step S120 to the step S121). The MME may re-authenticate theUE in the TAU procedure (the step S106).

ISR-related aspects in the foregoing TAU procedure are stipulated in theexisting specification (TS23.060 and TS23.401) as follows:

In the step S105, the SGSN transmits a Context Response message to theMME to instruct ISR to be activated; and

In the step S107, the SGSN receives a Context Acknowledgement message,transmitted from the MME, instructing ISR to be activated, and then theSGSN has to maintain a context of the UE.

The foregoing stipulations may result in a problem which will bedescribed below in connection with several related timers.

A mobile reachable timer of the UE is maintained at the network side,the mobile reachable timer is started when the UE enters an idle state,and the mobile reachable timer is stopped at the network side when theUE has a Non-Access Stratum (NAS) signalling connection established withthe network side (the UE enters a connected state); and

An implicit detach tinier of the UE is maintained at the network side,and if the mobile reachable timer expires and the UE has no NASsignalling connection established with the network side, the implicitdetach timer is started at the network side. An implicit detachprocedure is initiated at the network side after the implicit detachtimer expires. The implicit detach timer is stopped at the network sidewhen the UE has an NAS signalling connection established with thenetwork side.

The UE maintains a periodic TAU timer, or a periodic RAU timer, or aperiodic TAU timer and a periodic RAU timer dependent upon an accessscheme and an ISR state.

The UE with a UTRAN access has to maintain a periodic RAU timer when ISRis deactivated. The UE has to initiate a periodic RAU procedure when theperiodic RAU timer expires. The UE with an E-UTRAN access has tomaintain a periodic TAU timer when ISR is deactivated. The UE has toinitiate a periodic TAU procedure when the periodic TAU timer expires.The periodic TAU timer, or the periodic RAU timer, or the periodic TAUtimer and the periodic RAU timer are started when the UE enters an idlestate and stopped when the UE has an NAS signalling connectionestablished with the network.

The UE has to maintain both of the timers when ISR is activated. If theperiodic TAU timer expires when the UE resides in the UTRAN, the UE hasto start an E-UTRAN Deactivate ISR Timer, and the UE has to initiate aTAU procedure immediately upon next entry into the E-UTRAN. When theE-UTRAN Deactivate ISR Timer expires, the UE has to deactivate ISRlocally, that is, sets a TIN to a “P-TMSI”. The UE stops the E-UTRANDeactivate ISR Timer upon entering an EPS MobilityManagement-DEREGISTERED (EMM-DEREGISTERED) state or an EPS MobilityManagement-CONNECTED (EMM-CONNECTED) mode. If the periodic RAU timerexpires when the UE resides in the E-UTRAN, the UE has to start aGERAN/UTRAN Deactivate ISR Timer (GERAN stands for GSM EDGE Radio AccessNetwork. GSM stands for Global System for Mobile communication, and EDGEstands for Enhanced Data rates for GSM Evolution), and the UE has toinitiate an RAU procedure immediately upon next entry into the UTRAN.The UE has to deactivate ISR when the GERAN/UTRAN Deactivate ISR Timerexpires. The UE stops the GERAN/UTRAN Deactivate ISR Timer upon enteringa GPRS Mobility Management-DEREGISTERED (GMM-DEREGISTERED) state or aGMM-CONNECTED mode.

As stipulated in the existing specification, the mobile reachable timerhas a slightly larger timer length (that is, a timing period as meanthereinafter; and a timer length, a timing period, and a timer valuerefer to the same meaning) than that of the periodic TAU timer or theperiodic RAU timer. When ISR is activated, the Implicit Detach Timer atthe MME has a larger timer value than that of the E-UTRAN Deactivate ISRTimer of the UE, and the Implicit Detach Timer at the SGSN has a largertimer value than that of the GERAN/UTRAN Deactivate ISR Timer of the UE.

The UE initiating the RAU has to include a different identity in an RAUrequest dependent upon setting of a TIN. The RAU request includes only aPacket Temporary Mobile Station Identity (P-TMSI) when ISR is activated.When ISR is deactivated, the RAU request includes only a P-TMSI if theTIN is set to the P-TMSI. If the TIN is set to a Globally UniqueTemporary Identity (GUTI), the UE has to map the GUTI to a P-TMSI andinclude it in an RAU request message and shall also include the P-TMSIin the RAU request message if the UE is also provided with the P-TMSI,The SGSN can further search locally with the P-TMSI for a context of theUE upon reception of the request including the two temporary identities.

Thus the MME instructs the UE to activate ISR if the old SGSN stillinstructs the MME to activate ISR in the step S105 upon reception of acontext request message from the MME (the step S104) after the MobileReachable Timer of the UE expires and before the Implicit Detach Timerexpires. At this time, since the UE firstly is attached over the UTRANand its TIN is set to a P-TMSI, the UE will set the TIN to anRAT-related TMSI when the TAU Accept message instructs ISR to beactivated, if at this time the LIE goes from the E-UTRAN back to theUTRAN again and the UE determines that ISR is in an activated state,that is, the TIN is set to the RAT-related TMSI, the UE will initiatethe RAU with the P-TMSI. At this time the Implicit Detach Timermaintained by the SGSN may have expired, and since the SGSN initiatesthe implicit detach procedure after the Implicit Detach Timer expires,the context of the UE is absent at the SGSN at that time, so the SGSNcan not retrieve the context of the UE with the P-TMSI over the network.At this time the network will reject the RAU request of the UE, and theUE, has to reinitiate an attach procedure. The network can alsoreinitiate an authentication procedure. Inconsistency arises between theISR state indication at the UE side and the ISR state at the networkside (that is, a context maintenance condition of the UE at the networkside), thus resulting in a certain delay in an access of the UE over theUTRAN.

Furthermore, the SGSN has to maintain the context of the UE uponreception of the Context Acknowledgement message from the MME asmentioned in the step S107. However, a specific period of time for whichthe context of the UE is maintained is absent in the specification. Ifthe SGSN receives a Context Request message from the MME after theMobile Reachable Timer of the UE expires and before the Implicit DetachTimer expires, instructs the MME to activate ISR and continues withmaintaining the context of the UE after the Implicit Detach Timerexpires, then a great deal of useless context information arises in theSGSN, and a mechanism to clean such useless information is absent.

The foregoing problem can be addressed in such a method that ISR isdeactivated locally at the UE side. An underlying idea of this method isas follows:

-   -   1) In the UTRAN, the UE does not activate ISR or deactivates ISR        locally if the periodic TAU timer of the UE expires when the        network instructs the UE to activate ISR in the RAU. Thereafter        the TAU request message will include two temporary identities of        a P-TMSI and a GUTI when the UE accessing the E-UTRAN initiates        the TAU    -   2) In the E-UTRAN, the UE does not activate ISR or deactivates        ISR locally if the periodic RAU timer of the UE expires when the        network instructs the UE to activate ISR in the TAU. Thereafter        the RAU request message will include two temporary identities of        a P-TMSI and a GUTI when the UE accessing the UTRAN initiates        the RAU.

The problem of inconsistency between the context maintenance conditionindicated by the ISR state at the UE side and the real maintenancecondition may still arise in the foregoing method, and either the TAUrequest or the RAU request will include two identities due todeactivation of ISR when the UE accesses from one network to anothernetwork, thus wasting an air interface resource to some extent; and thetwo temporary identities have to be received at the network side forprocessing, thus increasing signalling overhead at the network side andtime delay in the TAU or RAU process.

SUMMARY OF THE INVENTION

The invention provides a method and network-side device for optimizingactivation/deactivation of ISR, an ISR operation method at the UE sideand a UE so as to optimize the existing ISR activation flow and ISRactivation method.

The invention provides a method for optimizing activation/deactivationof Idle State Signalling Reduction (ISR), which includes:

-   -   receiving, by a first network entity, a Context Request message        transmitted from a second network entity and deciding to        activate or deactivate ISR according to an operation state of a        mobile reachable timer and/or an implicit detach timer        corresponding to a UE in an area update procedure of the UE,        wherein the first network entity belongs to a first network and        the second network entity belongs to a second network; and    -   transmitting, by the first network entity, a decision result to        the second network entity, and the second network entity        instructing the UE to activate or deactivate ISR in response to        the received decision result.

The invention further provides an ISR operation method at the UE side,which includes:

-   -   receiving, by a. LIE, an ISR activation instruction transmitted        from the network side in an area update procedure of a second        network; and    -   starting or restarting, by the UE, a deactivate ISR timer of a        first network of the UE upon determining that a periodic area        update timer of the first network of the UE expires.

The invention further provides a first network-side device foroptimizing activation/deactivation of ISR in a first network, whichincludes:

-   -   a first activation deciding unit configured to decide to        activate or deactivate ISR according to an operation state of a        mobile reachable timer and/or an implicit detach timer        corresponding to a UE upon reception of a Context Request        message transmitted from a second network-side device in a        second network in an area update procedure of the UE; and    -   a transmitting unit configured to transmit a decision result to        the second network-side device.

The invention further provides a User Equipment (UE), which includes:

-   -   an instruction receiving unit configured to receive an ISR        activation instruction transmitted from the network side in an        area update procedure of a second network; and    -   a deactivate ISR timer restarting unit configured to start or        restart a deactivate ISR timer of a first network of the UE upon        determining that a periodic area update timer of the first        network of the UE expires upon reception of the ISR activation        instruction.

The invention has the advantageous effects of optimizing the existingISR activation and deactivation flows and ISR operation method at the UEside, of keeping highly consistent ISR processes at the network side andthe UE side and of avoiding unnecessary signalling overhead.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of an area update procedure stipulated theexisting specification;

FIG. 2 is a flow chart of a method for optimizingactivation/deactivation of ISR according to the invention;

FIG. 3 is a flow chart of a method for optimizingactivation/deactivation ISR according to an embodiment of the invention;

FIG. 4 is a flow chart of a method for optimizingactivation/deactivation of ISR in an application scenario according toan embodiment of the invention;

FIG. 5 is a flow chart of another method for optimizingactivation/deactivation of ISR according to an embodiment of theinvention;

FIG. 6 is flow chart of an ISR operation method at the UE side accordingto an embodiment of the invention;

FIG. 7 is a flow chart of another method for optimizingactivation/deactivation of ISR in an application scenario according toan embodiment of the invention;

FIG. 8 is a structural block diagram of a first network-side device foroptimizing activation/deactivation of ISR according to an embodiment ofthe invention; and

FIG. 9 is a structural diagram of a User Equipment (UE) according to anembodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A method and network-side device for optimizing activation/deactivationof ISR, an ISR operation method at the UE side and a UE according to theinvention will be described below in further details with reference tothe drawings and embodiments.

In order to address the situation in the prior art of inconsistencybetween ISR states at the network side and the UE side duringinteraction between an MME and an SGSN about whether to activate ISRbecause activation of ISR is decided as long as it is determined thatthe present network node supports activation of ISR, the inventionproposes a method for optimizing activation/deactivation of ISR, asillustrated in FIG. 2, which includes the following steps.

In the step S201, a first network entity decides to activate ordeactivate ISR according to an operation state of a mobile reachabletimer, or an implicit detach timer, or a mobile reachable timer and animplicit detach timer corresponding to a UE upon reception of a ContextRequest message transmitted from a second network entity in an areaupdate procedure of the UE.

Preferably, the area update procedure is a TAU procedure initiated bythe UE accessing a TA in an E-UTRAN from an RA in a UTRAN, and the firstnetwork entity is an SGSN and the second network entity is an MME;

Or the area update procedure is an RAU procedure initiated by the LIEaccessing an RA in a UTRAN from a TA in an E-UTRAN, and the firstnetwork entity is an MME and the second network entity is an SGSN.

In the step S202, the first network entity transmits a decision resultto the second network entity. The second network entity instructs the UEto activate or deactivate ISR in response to the received decisionresult. Preferably, the second network entity transmits the ISRactivation or deactivation instruction to the first network entity in aContext Acknowledgement message.

Particularly, the first network entity transmits the decision result tothe second network entity in a Context Response message, for example.

Preferably, when the area update procedure is the TAU procedureinitiated by the UE accessing the TA in the E-UTRAN from the RA in theUTRAN, the SGSN transmits the decision result to the MME; or

When the area update procedure is the RAU procedure initiated by the UEaccessing the RA in the UTRAN from the TA in the E-UTRAN, the MMEtransmits the decision result to the SGSN.

Particularly, the mobile reachable timer is maintained by the firstnetwork entity, started when the UE enters an idle state and stoppedwhen the UE enters a connected state, that is, has an NAS signallingconnection established with the first network entity, and its expirationresults in the start of the implicit detach timer; and the implicitdetach timer is maintained by the first network entity and stopped whenthe UE enters a connected state or the UE has an NAS signallingconnection established with the first network entity, and its expirationtriggers the first network entity to perform a detach procedure of theUE, and the detach procedure deletes a context of the UE maintained inthe first network entity.

In the invention, the first network entity decides whether to activateISR according to the operation states of its maintained mobile reachabletimer and implicit detach timer of the UE upon reception of the contextrequest instead of instructing ISR to be activated if the network nodesupports activation of ISR as in the existing flow. Those skilled in theart can appreciate that such a problem may arise that a context may beabsent if the UE gets back when ISR is activated because expiration ofthe mobile reachable timer may trigger the detach timer, and thisproblem can be avoided when it is decided whether to activate ISRaccording to the operation state of the mobile reachable timer, or theimplicit detach timer, or the mobile reachable timer and the implicitdetach timer.

Preferred embodiments of the invention will be given below.

As illustrated in FIG. 3, a method for optimizingactivation/deactivation of ISR according to a first embodiment of theinvention includes the following steps.

Step S301. A first network entity receives a Context Request messagetransmitted from a second network entity in an area update procedure ofa UE.

Step S302. The first network entity determines whether its maintainedmobile reachable timer of the UE expires, and if not, it performs thestep S303; and if so, it performs the step S304.

Step S303. The first network entity decides to activate ISR.

Since the mobile reachable timer does not expire, then an implicitdetach timer corresponding to the UE has not been started, and thestarted implicit detach timer has a larger timer length than that of adeactivate ISR timer of a first network of the UE if ISR is activated asper the existing specification, so when the UE gets back to the networkwhere the first network entity resides in an ISR activated state, acontext of the UE is still stored on the first network entity, and theproblem in the prior art of failing to retrieve the context of the UEwill not arise.

Step S304. The first network entity decides to deactivate ISR.

Alternatively, in the step S302 of this embodiment, it can be determinedwhether the implicit detach timer corresponding to the UE is running,and if not, the flow goes to the step S303; and if so, the flow goes tothe step S304.

Alternatively, it can be determined both whether the implicit detachtimer is running and whether the mobile reachable timer expires, and itis decided whether to activate or deactivate ISR according todetermination results.

The mobile reachable timer expires and this indicates that the implicitdetach timer is started, which means that the context of the UE will bedeleted after a period of time, so it is decided to deactivate ISR. Thusthe UE deactivates ISR upon reception of an ISR deactivationinstruction, and when the UE gets back to the network where the firstnetwork entity resides, ISR is not activated at either the network sideor the UE side, so such a situation will not arise that the context ofthe UE can not be retrieved with an identity provided by the UE at thenetwork side over the network.

It shall be noted here that deactivation of ISR as referred to in theinvention relates to two situations: the UE keeps ISR not activated whenISR is not activated in one situation and the UE deactivates ISR whenISR has been activated in the other situation.

A specific flow of the embodiment of the invention will be given belowin specific application scenarios.

In a first application scenario, the UE initiates an RAU upon accessingan RA in a UTRAN from a TA in an E-UTRAN, that is, the UE chooses toreside in the UTRAN.

As illustrated in FIG. 4, a flow of activation/deactivation by the UE inthis embodiment is as follows when the UE accesses over the E-UTRAN andis attached to an EPS and the UE reselects a cell to access the UTRAN.

Step S401. The UE transmits an RAU Request message to the SGSN, and aperiodic TAU timer of the UE expires before or after the message istransmitted.

Step S402. The SGSN receives the RAU Request message transmitted fromthe UE and transmits a Context Request message to the MME.

Step S403. The MIME receives the Context Request message transmittedfrom the SGSN and determines whether its maintained mobile reachabletimer of the UE expires.

The MME decides to activate ISR if the mobile reachable timercorresponding to the UE does not expire.

If the mobile reachable timer corresponding to the UE expires, theimplicit detach tinier shall not have expired as per the existing timerlength definition and flow, and the MME determines that the implicitdetach timer is running and then decides to deactivate ISR.

Step S404. The SGSN receives the result of deciding toactivate/deactivate ISR transmitted from the MME in a Context Responsemessage and decides to instruct ISR to be activated or deactivatedaccording to whether c network node supports activation of ISR as well.

Step S405. The SGSN transmits an ISR activation/deactivation instructionto the MME in a Context Acknowledgement message.

Step S406. The SGSN transmits the ISR activation/deactivationinstruction to the UE in an RAU Accept message, and accordingly the UEproceeds as in the existing ISR activation/deactivation flow.

Since it is decided to deactivate ISR when the mobile reachable timerexpires or the implicit detach timer is running, there is an ISRdeactivated state at the UE side. Thus the UE getting back to theE-UTRAN will initiate a TAU with only one temporary identity. There isan ISR deactivated state consistently both at the network side and atthe UE side. The situation can be avoided that the UE provides thenetwork with a temporary identity as if ISR is activated but the networkcan not locate a context of the UE with the temporary identity.

In a second application scenario, the UE initiates a TAU upon accessinga TA in an E-UTRAN from an RA in a UTRAN, that is, the UE chooses toreside in the E-UTRAN,

A flow of activation/deactivation by the UE in this embodiment is asfollows when the UE accesses over the UTRAN and is attached to an EPSand the UE reselects a cell to access E-UTRAN.

The UE transmits a TAU Request message to the MME.

The MME receives the TAU Request message transmitted from the UE andtransmits a Context Request message to the SGSN.

The SGSN receives the Context Request message transmitted from the MMEand determines whether its maintained mobile reachable timer of the UEexpires.

The SGSN decides to activate ISR if the mobile reachable timercorresponding to the UE does not expire.

If the mobile reachable timer corresponding to the UE expires, theimplicit detach timer shall not have expired as per the existing timerlength definition and flow, and the SGSN determines that the implicitdetach timer is running and then decides to deactivate ISR.

The MME receives the result of deciding to activate/deactivate ISRtransmitted from the SGSN in a Context Response message and decides toinstruct ISR to be activated or deactivated according to whether thenetwork node supports activation of ISR as well.

The MME transmits an ISR activation/deactivation instruction to the SGSNin a Context Acknowledgement message.

The MME transmits the ISR activation/deactivation instruction to the UEin an TAU Accept message, and accordingly the UE proceeds as in theexisting ISR activation/deactivation flow.

As illustrated in FIG. 5, another method for optimizingactivation/deactivation of ISR according to an embodiment of theinvention includes the following steps.

Step S501. A first network entity receives a Context Request messagetransmitted from a second network entity in an area update procedure ofa UE.

Step S502. The first network entity determines whether a mobilereachable timer corresponding to the UE expires, and if not, it performsthe step S503; and if so, it performs the step S504.

Step S503. The first network entity decides to activate ISR.

Since the mobile reachable timer does not expire, then an implicitdetach timer has not been started, and the implicit detach timer has alarger timer length than that of a deactivate ISR timer of a firstnetwork of the UE as per the existing specification, so when the UE getsback to the network where the first network entity resides in an ISRactivated state, a context of the UE is still stored on the firstnetwork entity, and the problem in the prior art of failing to retrievethe context of the UE will not arise.

Step S504. The first network entity decides to activate ISR andtransmits the result of deciding to activate ISR to the second networkentity.

Step S505, The second network entity receives the result of ISRactivation, and then if it is determined that the network node supportsactivation of ISR, it decides to instruct the UE to activate ISR andtransmits an ISR activation instruction to UE in an Area Update Acceptmessage and to the first network entity in a Context Acknowledgementmessage.

Particularly, the UE starts or stops and then starts the deactivate ISRtimer of the first network of the UE if a periodic area update timer ofthe first network of the UE expires when the UE receives the ISRactivation instruction transmitted from the second network.

“Stop and then start” as mentioned in the embodiment of the inventionrefers to “restart”, and thus “restart” will refer to “stop and thenstart” throughout the following embodiments.

Step S506. The first network entity receives the ISR activationinstruction returned from the second network entity, and then if theimplicit detach timer corresponding to the UE is running, it restartsthe implicit detach timer corresponding to the UE with a slightly largertimer length than that of the deactivate ISR timer of the first networkof the UE.

Alternatively, in the step S502, it can be decided whether to activateISR according to whether the implicit detach timer is running.

An area update timer of the first network is maintained by the UE,started when the UE goes into the idle state and stopped when the UEenters a connected state, that is, has an NAS signalling connectionestablished with the first network, and its expiration triggers the UEto initiate an area update.

The deactivate ISR timer of the first network is maintained by the UE,started when the area update timer of the first network expires and ISRis in an activated state and stopped when the UE enters a connectedstate, that is, has an NAS signalling connection established with thefirst network, and its expiration triggers the UE to deactivate ISR.

Preferably, the first network entity is a Mobility Management Entity(MME), the second network entity is a Serving GPRS Support Node (SGSN),the deactivate ISR timer of the first network of the UE is an E-UTRANdeactivate ISR timer, and the periodic area update timer of the firstnetwork is a periodic tracking area update timer; or

The first network entity is an SGSN, the second network entity is anMME, the deactivate ISR timer of the first network of the UE is aGERAN/UTRAN deactivate ISR timer, and the periodic area update tinier ofthe first network is a periodic routing area update timer.

That is, the first network corresponds to the first network entity, andthe second network corresponds to the second network entity.

When it is decided to instruct the UE to activate ISR, the UE and thefirst network entity start respectively the deactivate ISR timer of thefirst network and the implicit detach timer at the same time, and whenthe ISR is activated, the implicit detach timer has a larger timingperiod than that of the deactivate ISR timer of the first network as perthe existing specification, so the first network entity has not deletethe context of the UE if the deactivate ISR timer of the first networkof the UE does not expire when the UE gets back to the network where thefirst network entity resides. If the deactivate ISR timer of the firstnetwork of the UE expires, the UE has deactivated ISR, and no problemwill arise even if ISR is not deactivated at the network side.

An embodiment of the invention further provides an ISR operation methodado UE side, as illustrated in FIG. 6, which includes the followingsteps.

Step S601. A UE receives an ISR activation instruction transmitted fromthe network side in an area update procedure of a second network.

Step S602. The UE determines whether an area update timer of a firstnetwork expires, and if not, it performs the step S603; and if so, itperforms the step S604.

Step S603. The UE proceeds as in the existing flow, that is, activatesISR upon reception of an Area Update Accept message including ISRactivation instruction information. After the area update procedure isfinished, thus entering an idle state, a periodic area update timer ofthe second network is started, and when the area update timer expires inan idle state, a deactivate ISR timer of the second network is started.

Step S604, The UE starts or restarts a deactivate ISR timer of the firstnetwork of the UE.

Preferably, the area update procedure of the second network is a routingarea update procedure, the periodic area update timer of the firstnetwork is a periodic tracking area update timer, and the deactivate ISRtimer of the first network is an E-UTRAN deactivate. ISR timer; or

The area update procedure of the second network is a tracking areaupdate procedure, the periodic area update timer of the first network isa periodic routing area update timer, and the deactivate ISR timer ofthe first network is a GERAN/UTRAN deactivate ISR timer.

A specific flow of the embodiment of the invention will be given belowin specific application scenarios.

In a first application scenario, the UE initiates an RAU upon accessingan RA in a UTRAN from a TA in an E-UTRAN, that is, the UE chooses toreside in the UTRAN.

As illustrated in FIG. 7, a flow of activation/deactivation by the UE inthis embodiment is as follows when the UE accesses over the E-UTRAN andis attached to an EPS and the UE reselects a cell to access the UTRAN.

Step S701, The UE transmits an RAU Request message to the SGSN, aperiodic area update timer, TAU timer, of the UE expires at a certaininstance of time before or after the message is transmitted, and the UEhas not received an RAU Accept message at that instance of time.

Step S702. The SGSN receives the RAU Request message transmitted fromthe UE and transmits a Context Request message to the MME.

The MME receives the Context Request message transmitted from the SGSNand determines whether its maintained mobile reachable timer of the UEexpires and whether an implicit detach timer is running.

The MME decides to activate ISR if the mobile reachable timercorresponding to the UE does not expire, and the flow proceeds as in theexisting flow, so a detailed description thereof will be omitted here.

If the mobile reachable timer corresponding to the UE expires and theimplicit detach timer is running, it is decided to activate ISR, and thefollowing flow will be described in this scenario.

Step S703. The SGSN receives the result of deciding to activate ISRtransmitted from the MME in a Context Response message, and the SGSNperforms the step S704 upon deciding to instruct the UE to activate ISRaccording to whether the SGSN supports activation of ISR as well.

Step S704. The SGSN transmits an ISR activation instruction to the MMEin a Context Acknowledgement message.

Step 705. The MIME receives the ISR activation instruction in theContext Acknowledgement message, and then if the implicit detach timercorresponding to the UE is running, it restarts the implicit detachtimer corresponding to the UE at a slightly larger timing period thanthat of an E-UTRAN deactivate ISR timer of the UE.

Step S706. The SGSN transmits the ISR activation instruction to the UEin an RAU Accept message.

Step 707. The UE receives the RAU Accept message including the ISRactivation instruction and then determines whether the periodic trackingarea update timer of the UE expires, and if so, it starts or restartsthe E-UTRAN deactivate ISR timer of the UE.

In a second application scenario, the UE initiates a TAU upon accessinga TA in an E-UTRAN from an RA in a UTRAN, that is, the UE chooses toreside in the E-UTRAN.

A flow of activation/deactivation by the UE in this embodiment is asfollows When the UE accesses over the UTRAN and is attached to an EPSand the UE reselects a cell to access the E-UTRAN.

The UE transmits a TAU Request message to the MME, a periodic areaupdate timer, RAU timer, of the UE expires before or after the messageis transmitted, and the UE has not received a TAU Accept message at thetime of expiration.

The MME receives the TAU Request message transmitted from the UE andtransmits a Context Request message to the SGSN.

The SGSN receives the Context Request message transmitted from the MMEand determines Whether its maintained mobile reachable timer of the UEexpires and whether an implicit detach timer is running.

The SGSN decides to activate ISR if the mobile reachable timercorresponding to the UE does not expire, and the flow proceeds as in theexisting flow, so a detailed description thereof will be omitted here.

If the mobile reachable timer corresponding to the UE expires and theimplicit detach timer is running it is decided to activate ISR, and thefollowing flow will be described in this scenario.

The MME receives the result of deciding to activate ISR transmitted fromthe SGSN in a Context Response message, and the MME transmits an ISRactivation instruction to the SGSN in a Context Acknowledgement messageupon deciding to instruct the UE to activate ISR according to whetherthe MME supports activation of ISR as well.

The SGSN receives the ISR activation instruction in the ContextAcknowledgement message, and then if the implicit detach timercorresponding to the UE is running, it restarts the implicit detachtinier corresponding to the UE at a slightly larger timing period thanthat of a GERNA/UTRAN deactivate ISR timer of the UE.

The MME transmits the ISR activation instruction to the UE in a TAUAccept Message.

The UE receives the TAU Accept message including the ISR activationinstruction and Then determines whether the periodic routing area updatetimer of the UE expires, and if so, it starts or restarts theGERNA/UTRAN deactivate ISR timer of the UE.

There is provided in a third embodiment of the invention a firstnetwork-side device for optimizing activation/deactivation of ISR, asillustrated in FIG. 8, which includes:

-   -   a first activation deciding unit 801 configured to decide to        activate or deactivate ISR according to an operation state of a        mobile reachable timer and/or an implicit detach timer        corresponding to a UE upon reception of a Context Request        message transmitted from a second network-side device in an area        update of the UE; and    -   a transmitting unit 802 configured to transmit a decision result        to the second network-side device.

Preferably, the first activation deciding unit 801 is further configuredto decide to deactivate ISR when the mobile reachable timercorresponding to the UE expires or decide to deactivate ISR when theimplicit detach timer corresponding to the UE is running; or

The first activation deciding unit 801 is further configured to decideto activate; ISR after the mobile reachable timer corresponding to theUE expires and when the implicit detach timer corresponding to the UE isrunning; and the first network-side device further includes: a detachtimer restarting unit 803 configured to restart the implicit detachtimer corresponding to the UE upon determining that the implicit detachtimer corresponding to the UE is running when an ISRactivation/deactivation instruction returned from the secondnetwork-side device is determined as an ISR activation instruction.

And the first activation deciding unit 801 is further configured todecide to activate ISR when the mobile reachable timer corresponding tothe UE does not expire.

In this embodiment, the restarted implicit detach timer has a largertiming period than that of a deactivate ISR timer of a first network ofthe UE.

The first network-side device is a Mobility Management Entity (MME), thesecond network-side device is a Serving GPRS Support Node (SGSN), andthe deactivate ISR timer of the first network of the UE is an E-UTRANdeactivate ISR timer; or

The first network-side device is an SGSN, the second network-side deviceis an MME, and the deactivate ISR timer of the first network of the UEis a GERAN/UTRAN deactivate ISR timer.

There is further provided in an embodiment of the invention a UserEquipment (UE), as illustrated in FIG. 9, which includes:

-   -   an instruction receiving unit 901 configured to receive an ISR        activation instruction transmitted from the network side in an        area update procedure of a second network; and    -   a deactivate ISR timer restarting unit 902 configured to start        or restart a deactivate ISR timer of a first network of the UE        upon determining that a periodic area update timer of the first        network of the UE expires upon reception of the ISR activation        instruction.

Preferably, the area update procedure of the second network is a routingarea update procedure, the periodic area update tinier of the firstnetwork is a periodic tracking area update timer, and the deactivate ISRtimer of the first network is an E-UTRAN deactivate ISR timer; or

The area update procedure of the second network is a tracking areaupdate procedure, periodic area update timer of the first network is aperiodic routing area update timer, and the deactivate ISR timer of thefirst network is a GERAN/UTRAN deactivate ISR timer.

Those skilled in the art shall appreciate that the embodiments of theinvention can be embodied as a method, a system or a computer programproduct. Therefore the invention can be embodied in the form of anall-hardware embodiment, an all-software embodiment or an embodiment ofsoftware and hardware in combination. Furthermore, the invention can beembodied in the form of a computer program product embodied in one ormore computer useable storage mediums (including but not limited to adisk memory an optical memory, etc.) in which computer useable programcodes are contained.

The invention has been described in a flow chart and/or a block diagramof the method, device (system) and the computer program productaccording to the embodiments of the invention. It shall be appreciatedthat respective flows and/or blocks in the flow chart and/or the blockdiagram and combinations of the flows and/or the blocks in the flowchart and/or the block diagram can be embodied in computer programinstructions, These computer program instructions can be loaded onto ageneral-purpose computer, a specific-purpose computer, an embeddedprocessor or a processor of another programmable data processing deviceto produce a machine so that the instructions executed on the computeror the processor of the other programmable data processing device createmeans for performing the functions specified in the flow(s) of the flowchart and/or the block(s) of the block diagram.

These computer program instructions can also be stored into a computerreadable memory capable of directing the computer or the otherprogrammable data processing device to operate in a specific manner sothat the instructions stored in the computer readable memory create anarticle of manufacture including instruction means which perform thefunctions specified in the flow(s) of the flow chart and/or the block(s)of the block diagram.

These computer program instructions can also be loaded onto the computeror the other programmable data processing device so that a series ofoperational steps are performed on the computer or the otherprogrammable data processing device to create a computer implementedprocess so that the instructions executed on the computer or the otherprogrammable data processing device provide steps for performing thefunctions specified in the flow(s) of the flow chart and/or the block(s)of the block diagram.

Evidently those skilled in the art can make various modifications andvariations to the invention bout departing from the scope of theinvention. Thus the invention is also intended to encompass thesemodifications and variations thereto so long as the modifications andvariations come into the scope of the claims appended to the inventionand their equivalents.

The invention claimed is:
 1. A method for optimizingactivation/deactivation of Idle State Signalling Reduction, ISR,comprising: receiving, by a first network entity, a Context Requestmessage transmitted from a second network entity and deciding toactivate or deactivate ISR according to an operation state of a mobilereachable timer, or an implicit detach timer, or a mobile reachabletimer and an implicit detach timer corresponding to a UE in an areaupdate procedure of the UE, wherein the first network entity belongs toa first network and the second network entity belongs to a secondnetwork; and transmitting, by the first network entity, a decisionresult to the second network entity, and the second network entityinstructing the UE to activate or deactivate ISR in response to thereceived decision result.
 2. The method according to claim 1, whereinthe first network entity deciding to activate or deactivate ISRaccording to an operation state of a mobile reachable timer, or animplicit detach timer, or a mobile reachable timer and an implicitdetach timer corresponding to a UE further comprises: deciding todeactivate ISR when the mobile reachable timer corresponding to the UEexpires; or deciding to deactivate ISR when the implicit detach timercorresponding to the UE is running; or deciding to deactivate ISR whenthe mobile reachable timer corresponding to the UE expires and theimplicit detach timer corresponding to the UE is running.
 3. The methodaccording to claim 1, wherein the first network entity deciding toactivate or deactivate ISR according to an operation state of a mobilereachable timer, or an implicit detach timer, or a mobile reachabletimer and an implicit detach timer corresponding to a UE furthercomprises: deciding to activate ISR when the mobile reachable timercorresponding to the UE expires and the implicit detach timercorresponding to the UE is running.
 4. The method according to claim 1,further comprising: restarting, by the first network entity, theimplicit detach timer corresponding to the UE when an ISR activation ordeactivation instruction returned from the second network entity isdetermined as an ISR activation instruction.
 5. The method according toclaim 4, wherein the restarted implicit detach timer corresponding tothe UE has a larger timer length than that of a deactivate ISR timer ofthe first network of the UE.
 6. The method according to claim 1, furthercomprising: restarting, by the UE, a deactivate ISR timer of the firstnetwork of the UE if a periodic area update timer of the first networkof the UE expires upon reception of an ISR activation instructiontransmitted from the second network entity.
 7. The method according toclaim 1, wherein the area update procedure is a routing area updateprocedure, the first network entity is a Mobility Management Entity,MME, and the second network entity is a Serving GPRS Support Node, SGSN;or the area update procedure is a tracking area update procedure, thefirst network entity is an SGSN, and the second network entity is anMME.
 8. The method according to claim 7, wherein a deactivate ISR timerof the first network of the UE is an E-UTRAN deactivate ISR timer, and aperiodic area update timer of the first network of the UE is a periodictracking area update timer when the area update procedure is a routingarea update procedure; or a deactivate ISR timer of the first network ofthe UE is a GERAN/UTRAN deactivate ISR timer, and a periodic area updatetimer of the first network of the UE is a periodic routing area updatetimer when the area update procedure is a tracking area updateprocedure.
 9. The method according to claim 1, wherein the first networkentity deciding to activate or deactivate ISR according to an operationstate of a mobile reachable timer, or an implicit detach timer, or amobile reachable timer and an implicit detach timer corresponding to aUE further comprises: deciding to activate ISR when the mobile reachabletimer corresponding to the UE does not expire.
 10. A first network-sidedevice for optimizing activation/deactivation of ISR in a first network,comprising: a first activation deciding unit configured to decide toactivate or deactivate ISR according to an operation state of a mobilereachable timer, or an implicit detach timer, or a mobile reachabletimer and an implicit detach timer corresponding to a UE upon receptionof a Context Request message transmitted from a second network-sidedevice in a second network in an area update procedure of the UE; and atransmitting unit configured to transmit a decision result to the secondnetwork-side device.
 11. The device according to claim 10, wherein thefirst activation deciding unit is further configured to decide todeactivate ISR when the mobile reachable timer corresponding to the UEexpires or decide to deactivate ISR when the implicit detach timercorresponding to the UE is running.
 12. The device according to claim10, wherein the first activation deciding unit is further configured todecide to activate ISR after the mobile reachable timer corresponding tothe UE expires and when the implicit detach timer corresponding to theUE is running; or wherein the first activation deciding unit is furtherconfigured to decide to activate ISR when the mobile reachable timercorresponding to the UE does not expire.
 13. The device according toclaim 10, wherein the first network-side device further comprises: adetach timer restarting unit configured to restart the implicit detachtimer corresponding to the UE upon determining that an ISRactivation/deactivation instruction returned from the secondnetwork-side device is determined as an ISR activation instruction. 14.The device according to claim 13, wherein the restarted implicit detachtimer corresponding to the UE has a larger timer length than that of adeactivate ISR timer of the first network of the UE.
 15. The deviceaccording to claim 10, wherein the area update procedure is a routingarea update procedure, the first network-side device is a MobilityManagement Entity, MME, and the second network-side device is a ServingGPRS Support Node, SGSN; or the area update procedure is a tracking areaupdate procedure, the first network-side device is an SGSN, and thesecond network-side device is an MME.
 16. The device according to claim15, wherein: a deactivate ISR timer of the first network of the UE is anE-UTRAN deactivate ISR timer when the area update procedure is a routingarea update procedure; or a deactivate ISR timer of the first network ofthe UE is a GERAN/UTRAN deactivate ISR timer when the area updateprocedure is a tracking area update procedure.